1. Field of the Invention
The present invention relates to a method for wireless data transmission between a base station and a transponder, and to a transponder.
2. Description of the Background Art
Contactless identification systems, or so-called radio frequency identification (RFID) systems typically have a base station or reader (or reader unit) and a plurality of transponders or remote sensors. The transponders and their transmitting and receiving devices customarily do not have an active transmitter for data transmission to the base station. Such non-active systems are called passive systems if they do not have their own energy supply, and semi-passive systems if they have their own energy supply. Passive transponders take the energy they require for their supply from the electromagnetic field emitted by the base station.
For data transmission between the transponder and the base station, the transponder has an interface of a certain interface type, which is compatible with the corresponding interface type of the base station. In a first, rough categorization, the interface types can be divided into contacting and contactless types.
The interface types in which the data transmission takes place in a contactless way are distinguished, among other characteristics, by the operating or carrier frequency used for data transmission, which is to say the frequency transmitted by the base station. Commonly used frequencies include 125 kHz (LF range), 13.56 MHz (RF range), a frequency range between 860 MHz and 960 MHz (UHF range), and a frequency range above 3 GHz (microwave range).
Another distinguishing feature of different interface types is the type of coupling between the respective interfaces of the transponder and base station. In this regard, a distinction is made between what is called inductive or magnetic coupling and what is called far-field coupling, among others. In simplified terms, with inductive or near-field coupling an antenna coil of the base station and an antenna coil of the transponder form a transformer, for which reason this coupling type is also called transformer coupling. In the case of inductive coupling, a maximum separation between the transponder and the base station is limited to the region of a near field of the antennas used. The near field region is primarily determined by the operating frequency of the interface.
Far-field coupling relies on the propagation of electromagnetic waves which are emitted by the antenna used. UHF and microwave systems typically rely on far-field coupling. RF and HF systems, in contrast, typically rely on inductive coupling. Fundamentals in this regard can be found in, for example, the “RFID Handbuch,” a textbook by Klaus Finkenzeller, HANSER Verlag, third edition, 2002, section 2.3, “Frequenz, Reichweite Kopplung” (Frequency, Range and Coupling), section 3.2.1, “Induktive Kopplung” (Inductive Coupling), and section 4.2.1.1, “Übergang vom Nah-zum Fernfeld bei Leiterschleifen” (Transition from Near Field to Far Field in Conductive Loops).
In general, load modulation is used to transmit data from a transponder to the base station in the case of inductive coupling; for information on this, refer to Finkenzeller, section 3.2.1.2.1, “Lastmodulation” (Load Modulation), for example.
In general, backscatter coupling is used to transmit data from a transponder to the base station using UHF or microwaves in the far field of the base station. To this end, the base station emits electromagnetic carrier waves, which the transmitting and receiving device in the transponder modulates and reflects appropriately for the data to be transmitted to the base station using a modulation method. The typical modulation methods for this purpose are amplitude modulation, phase modulation and amplitude shift keying (ASK) subcarrier modulation, in which the frequency or the phase position of a subcarrier is changed; in this regard, refer once again to Finkenzeller, section 3.2.2, “elektromagnetische Backscatter-Kopplung” (Electromagnetic Backscatter Coupling).
Data transmission protocols are used for data transmission. A data transmission protocol specifies, for example, an operating frequency, a modulation method, a coding method, data transmission rates, data transmission frame formats, transmission parameters, etc.
Data transmission protocols are typically divided into different layers. One example of this is known as the OSI layer model, with seven data transmission protocol layers. The different layers here are referred to as the physical layer (layer 1), the data link layer (layer 2), the network layer (layer 3), the transport layer (layer 4), the session layer (layer 5), the presentation layer (layer 6), and the application layer (layer 7). For a more detailed description of the OSI model, reference is made to the literature identified above.
In transponders, the data transmission protocols are interface-specific, or in other words, each interface type is assigned its own, proprietary data transmission protocol. Thus, for instance, a transmission protocol for transponders with a UHF interface with far-field coupling in the frequency range of 860 MHz to 960 MHz is described in the proposed standard ISO/IEC_CD 18000-6C dated Jan. 7, 2005. For transponders with an HF interface with inductive coupling with a frequency of 13.56 MHz, a transmission protocol is described in ISO standard 14443. In this context, the data transmission protocols differ significantly across all protocol layers.
In WO 2005/109328 A1, which corresponds to U.S. Publication No. 20050237163, a transponder for so-called remote keyless applications is described which has an active, unidirectional interface for the UHF frequency range and multiple bidirectional interfaces for the LF frequency range. The UHF interface and the relevant LF interfaces use different, proprietary data transmission protocols. Because of the different data transmission protocols, uniform processing within a shared protocol stack of the data that is received or transmitted is not possible.